1. Field of the Invention
This invention relates to an electronic control fuel supply system for use in controlling the air-fuel ratio of the mixture of air and fuel being supplied to an internal combustion engine.
2. Description of the Prior Art
In a known electronic control fuel supply system, a .lambda. sensor is utilized to detect the actual air-fuel ratio of the mixture being supplied to an engine. Report No. 730566 of The Society of Automotive Engineers discloses a detailed arrangement of a .lambda. sensor positioned in the exhaust system of an engine, the .lambda. sensor being one type of oxygen sensor. The output voltage of the .lambda. sensor varies in a digital manner as the air-fuel ratio of the mixture supplied to the internal combustion engine changes between values lower and higher than the predetermined stoichiometric air-fuel ratio.
The input of an integrating circuit in the electronic control fuel supply system is connected to the output of the .lambda. sensor, and the output of the integrating circuit is connected to a fuel injection valve which injects fuel into the intake system of the engine. In this connection, the air-fuel ratio control is subjected to a hunting phenomenon because a time lag occurs between the variation of the air-fuel ratio of the introduced mixture and the variation in output voltage of the .lambda. sensor; i.e., there is a dead time for the response of this control system.
If the level of hunting is to be minimized, the time constant of the integrating circuit must be set to an optimum value. However, it is difficult to achieve compatibility between the follow-up characteristics of the actual air-fuel ratio and the stoichiometric air-fuel ratio during the transient phase of the engine.